Method for augmenting radio positioning system using single fan laser

ABSTRACT

A method of augmenting a mobile radio positioning system (Mobile_RADPS) by using a stationary fan laser transmitter. A rover comprises the mobile radio positioning system (Mobile_RADPS) integrated with a mobile laser detector. The stationary fan laser transmitter is integrated with a stationary radio positioning system (Stationary_RADPS). The method comprises the following steps: (A)generating a single sloping fan beam by the stationary fan laser transmitter; (B) detecting the single sloping fan beam generated by the stationary fan laser transmitter by using the mobile laser detector; and (C) timing the fan laser beam strike at the rover&#39;s location and using the timing of the fan laser beam strike at the rover&#39;s location to improve an accuracy in determination of position coordinates of the rover.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention is in the field of position tracking and machinecontrol systems, and, more specifically, is directed to augmenting aradio positioning system using a single fan laser system.

2. Discussion of the Prior Art

The combination of a radio-based positioning system, that can providethe centimeter accuracy in the best case scenario (RTK GPS) and alaser-based positioning system, that can provide a millimeter verticalcoordinate accuracy, is intended to improve the vertical accuracy of thecombined radio-light based positioning systems up to millimeters.

However, the prior art system utilize a fan laser generating at leasttwo laser beams to provide information to a radio-based positioningsensor.

SUMMARY OF THE INVENTION

The present invention discloses simplified scheme that makes use of theprecise timing of the radio-based positioning component of the combinedradio and light based positioning system. This allows one to use aprecisely timed single fan beam (instead of dual inclined laser fanbeams) to improve the vertical accuracy of the combined radio and lightbased positioning system.

One aspect of the present invention is directed to a method ofaugmenting a mobile radio positioning system (Mobile_RADPS) by using astationary fan laser transmitter.

In one embodiment, the method of the present invention comprises thefollowing steps: (A)generating a single sloping fan beam by thestationary fan laser transmitter; (B) detecting the single sloping fanbeam generated by the stationary fan laser transmitter by using themobile laser detector; and (C) timing the fan laser beam strike at therover's location and using the timing of the fan laser beam strike atthe rover's location to improve an accuracy in determination of positioncoordinates of the rover. In this embodiment of the present invention, arover comprises the mobile radio positioning system (Mobile_RADPS)integrated with a mobile laser detector. In this embodiment of thepresent invention, the stationary fan laser transmitter is integratedwith a stationary radio positioning system (Stationary_RADPS).

In one embodiment of the present invention, the step (A) of generatingthe single sloping fan beam by the stationary fan laser transmitterfurther comprises the following steps: (A1) providing the stationary fanlaser transmitter positioned in a location with known coordinates; and(A2) rotating the fan laser transmitter about its vertical axis at asubstantially constant angular rate.

In one embodiment of the present invention, the step (A1) of providingthe stationary fan laser transmitter positioned in the location withknown coordinates further comprises the step (A1, 1) of self-surveyingthe stationary fan laser transmitter to determine its positioncoordinates by using the stationary radio positioning system(Stationary_RADPS).

In one embodiment of the present invention, the step of (A1, 1) furthercomprises the step (A1, 1, 1) of receiving a first plurality of externalradio signals broadcasted by at least one radio source selected from thegroup consisting of: {GPS; GLONASS; combined GPS/GLONASS; GALILEO;Global Navigational Satellite System (GNSS) positioning system; and apseudolite transmitter} by using the stationary radio positioning system(Stationary_RADPS). In this embodiment of the present invention, thestationary radio positioning system (Stationary_RADPS) is configured toutilize the first plurality of external radio signals to obtain positioncoordinates of the stationary fan laser transmitter.

In one embodiment of the present invention, the step (A1, 1) furthercomprises the following steps: (A1, 1, 2) providing a differentialstationary radio positioning system (Stationary_RADPS); (A1, 1, 3)receiving a first plurality of external radio signals broadcasted by atleast one radio source selected from the group consisting of: {GPS;GLONASS; combined GPS/GLONASS; GALILEO; Global Navigational SatelliteSystem (GNSS); and a pseudolite transmitter} by using the differentialstationary radio positioning system (Stationary_RADPS); and (A1, 1, 4)receiving a first set of differential corrections data broadcasted by atleast one source selected from the group consisting of: {a Base Station,an RTK Base Station; a Virtual Base Station (VBS); and a pseudolitetransmitter by using the differential stationary radio positioningsystem (Stationary_RADPS). In this embodiment of the present invention,the differential stationary radio positioning system (Stationary_RADPS)is configured to utilize the first plurality of external radio signalsand the first set of differential corrections data to obtain positioncoordinates of the stationary fan laser transmitter.

In one embodiment of the present invention, the step of (A1, 1) furthercomprises the step (A1, 1, 5) of providing a wireless communication linkconfigured to connect the differential stationary radio positioningsystem (Stationary_RADPS) to the source of differential correction data.In this embodiment of the present invention, wherein the wirelesscommunication link is selected from the group consisting of: {a cellularlink; a radio; a private radio band; a SiteNet 900 private radionetwork; a wireless Internet; a satellite wireless communication link;and an optical wireless link}.

In one embodiment of the present invention, the step (A2) of rotatingthe fan laser transmitter about its vertical axis further comprises thestep (A2, 1) of mechanically rotating the fan laser transmitter headabout its vertical axis at the substantially constant angular rate. Inthis embodiment of the present invention, the substantially constantangular rate of the rotation of the fan laser transmitter head about itsvertical axis can be controlled by using a phase oscillator. In thisembodiment of the present invention, the substantially constant angularrate of the rotation of the fan laser transmitter head about itsvertical axis can be enhanced by giving the laser transmitter head asubstantially sufficient mass.

In one embodiment of the present invention, the step (A2) of rotatingthe fan laser transmitter about its vertical axis further comprises thestep (A2, 2) of optically rotating the fan laser transmitter about itsvertical axis at the substantially constant angular rate.

In one embodiment of the present invention, the step (A) of generatingthe single sloping fan beam by the stationary fan laser furthercomprises the following steps: (A3) generating an electronic timingpulse every time a known position of the laser beam passes a referencemark in the laser transmitter; (A4) time-tagging each electronic timingpulse by using the stationary radio positioning system(Stationary_RADPS); (A5) generating an estimate of an angular rate ofthe laser beam by using a plurality of time tags, wherein each time tagis indicative of a time instant when the reference mark is crossed by anelectronic timing pulse; and (A6) transmitting the estimate of theangular rate of the laser beam and the plurality of time tags to therover via a wireless communication link.

In one embodiment of the present invention, the wireless communicationlink comprises a first wireless communication link. In anotherembodiment of the present invention, the wireless communication linkcomprises a second wireless communication link.

In one embodiment of the present invention, the step (A5) of generatingan estimate of an angular rate of the laser beam by using a plurality oftime tags, wherein each time tag is indicative of a time instant whenthe reference mark is crossed by an electronic timing pulse furthercomprises the step (A5, 1) of generating a low-pass filtered estimate ofan angular rate of the laser beam by using a plurality of time tags,wherein each time tag is indicative of a time instant when the referencemark is crossed by an electronic timing pulse.

In one embodiment of the present invention, the step (A) of generatingthe single sloping fan beam by the stationary fan laser furthercomprises the following steps: (A7) including at least one additionalreference mark in addition to a main reference mark; (A8) generating anelectronic timing pulse every time a known position of the laser beampasses the main reference mark and each additional reference mark in thelaser transmitter; (A9) time-tagging each electronic timing pulse byusing the stationary radio positioning system (Stationary_RADPS); (A10)generating an estimate of an angular rate of the laser beam by using aplurality of time tags, wherein each time tag is indicative of a timeinstant when the main reference mark is crossed by an electronic timingpulse, or when each additional reference mark is crossed by anelectronic timing pulse; and (A11) transmitting the estimate of theangular rate of the laser beam and the plurality of time tags to therover via the wireless communication link; wherein a plurality of timetags defined by time-tagging the laser beam to each additional referencemark comprises a laser correction data that is configured to compensatefor variation of the rotation angular speed of the laser beam.

In one embodiment of the present invention, the step (A10) of generatingthe estimate of the angular rate of the laser beam by using a pluralityof time tags further comprises the step (A10, 1) of generating alow-passed filtered estimate of the angular rate of the laser beam byusing a plurality of time tags, wherein each time tag is indicative of atime instant when the main reference mark is crossed by an electronictiming pulse, or when each additional reference mark is crossed by anelectronic timing pulse.

In one embodiment of the present invention, the step (B) of detectingthe single sloping fan beam generated by the stationary fan lasertransmitter by using the mobile laser detector further comprises thefollowing steps: (B1) detecting at least one light pulse generated bythe laser transmitter by using a mobile laser detector; and (B2)receiving the estimate of the angular rate of the laser beam and theplurality of time tags by the rover. In this embodiment of the presentinvention, each light pulse corresponds to a single sloping fan laserbeam strike at the rover's location. In this embodiment of the presentinvention, the leading and/or trailing edges of each light pulse aretime-tagged by the stationary radio positioning system(Stationary_RADPS).

In one embodiment of the present invention, the step (B2) of receivingthe estimate of the angular rate of the laser beam and the plurality oftime tags by the rover further comprises the step of (B2, 1) ofreceiving the low-passed filtered estimate of the angular rate of thelaser beam and the plurality of time tags by the rover.

In one embodiment of the present invention, the step (B2, 1) furthercomprises the step (B2, 1, 1) of using the wireless communication linkto receive the low-passed filtered estimate of the angular rate of thelaser beam and the plurality of time tags by the rover.

In one embodiment of the present invention, the step (B) of detectingthe single sloping fan beam generated by the stationary fan lasertransmitter by using the mobile laser detector further comprises thefollowing steps: (B3) detecting at least one light pulse generated bythe laser transmitter by using the mobile laser detector; wherein eachlight pulse corresponds to a single sloping fan laser beam strike at therover's location; (B4) receiving the estimate of the angular rate of thelaser beam and the plurality of time tags by the rover; wherein theleading and/or trailing edges of each light pulse are time-tagged by thestationary radio positioning system (Stationary_RADPS); and (B5)receiving the laser correction data configured to compensate forvariation of the rotation angular speed of the laser beam; wherein thelaser correction data comprises a plurality of time tags defined bytime-tagging the laser beam to each additional reference mark.

In one embodiment of the present invention, the step (B4) furthercomprises the step (B4, 1) of receiving the low-passed filtered estimateof the angular rate of the laser beam and the plurality of time tags bythe rover; wherein the leading and/or trailing edges of each light pulseare time-tagged by the stationary radio positioning system(Stationary_RADPS). In this embodiment of the present invention, thewireless communication link is used by the rover to receive thelow-passed filtered estimate of the angular rate of the laser beam, toreceive the plurality of time tags, and to receive the laser correctiondata.

In one embodiment of the present invention, the step (C) of timing thefan laser beam strike at the rover's location and using the timing ofthe fan laser beam strike at the rover's location to improve theaccuracy in determination of position coordinates of the rover furthercomprises the following steps: (C1) measuring the time differencebetween the time instance when the light pulse corresponding to thesingle sloping fan laser beam strike at the rover's location is receivedand the latest main reference crossing time corresponding to the timeinstance when the center of the laser beam passes the main referencemark at the location of the laser transmitter; and (C2) calculating aheight of the rover with improved accuracy based on position coordinatesof the rover and based on the time difference measured at the step (C1);wherein the position coordinates of the rover are interpolated positioncoordinates interpolated between position coordinates taken at GPS timeEpoch immediately preceding the laser strike and position coordinatestaken at GPS time Epoch immediately after the laser strike.

In one embodiment of the present invention, the step (C2) furthercomprises the following steps: (C2, 1) providing a differential mobileradio positioning system (Mobile_RADPS); (C2, 2) receiving a secondplurality of external radio signals broadcasted by at least one radiosource selected from the group consisting of: {GPS; GLONASS; combinedGPS/GLONASS; GALILEO; Global Navigational Satellite System (GNSS); and apseudolite transmitter} by using the differential mobile radiopositioning system (Mobile_RADPS); and (C2, 3) receiving a second set ofdifferential corrections data broadcasted by at least one sourceselected from the group consisting of: {a Base Station, an RTK BaseStation; a Virtual Base Station (VBS) and a pseudolite transmitter} byusing the differential mobile radio positioning system (Mobile_RADPS).

In one embodiment of the present invention, the step (C2) furthercomprises the step (C3) of optimizing the improved height calculation ofthe rover.

In one embodiment of the present invention, the step (C3) of optimizingthe improved height calculation of the rover further comprises the step(C3, 1) of calculating a set of sensitivity parameters selected from thegroup consisting of: {a partial derivative of the rover's height withrespect to a laser beam rotation frequency; a partial derivative of therover's height with respect to a horizontal distance from the rover tothe laser transmitter; a partial derivative of the rover's height withrespect to a time difference between the actual laser strike time andthe expected laser strike time; and a partial derivative of the rover'sheight with respect to a vertical angle}.

In one embodiment of the present invention, the step (C3) furthercomprises the step (C3, 2) of calculating the variable laser beamrotation frequency by using the plurality of time tags corresponding totime-tagging of the laser beam to each additional reference mark at thelaser transmitter location.

In one embodiment of the present invention, the step (C) of timing thefan laser beam strike at the rover's location and using the timing ofthe fan laser beam strike at the rover's location to improve theaccuracy in determination of position coordinates of the rover furthercomprises the step (C4) of calibrating the improved height calculationof the rover for planar errors affecting the planarity of the fan beam.

In one embodiment of the present invention, the method of augmenting themobile radio positioning system (Mobile_RADPS) by using the stationaryfan laser transmitter further comprises the step (D) of determining withimproved accuracy position coordinates of an implement, wherein theimplement is selected from the group consisting of: {a blade or a bucketon an earthmoving machine; an agricultural implement; and a deviceconnected to a machine, wherein the device's location is beingcontrolled}.

In one embodiment of the present invention, the step (D) furthercomprises the step (D1) of controlling the movement of the implement.

Another aspect of the present invention is directed to a radio and lightbased mobile positioning system comprising: (A) a means for generating asingle sloping fan beam; (B) a means for detecting the single slopingfan beam at a rover's location, wherein the rover includes the mobilepositioning system; (C) a means for timing the fan laser beam strike atthe rover's location; and (D) a means for using the timing of the fanlaser beam strike at the rover's location to improve an accuracy indetermination of position coordinates of the rover.

In one embodiment, the system of the present invention further comprisesa rover including an implement. In this embodiment, the system of thepresent invention further comprises a means (E) for using the timing ofthe fan laser beam strike at the rover's location to improve an accuracyin determination of position coordinates of the implement.

In one embodiment of the present invention, the means (E) furthercomprises a means (E1) for controlling the movement of the implement.

BRIEF DESCRIPTION OF DRAWINGS

The aforementioned advantages of the present invention as well asadditional advantages thereof will be more clearly understoodhereinafter as a result of a detailed description of a preferredembodiment of the invention when taken in conjunction with the followingdrawings.

FIG. 1 depicts a radio and light based mobile positioning system of thepresent invention comprising a stationary fan laser transmitterintegrated with a stationary radio positioning system(Stationary_RADPS), and a rover further comprising a mobile radiopositioning system (Mobile_RADPS) integrated with a mobile laserdetector.

FIG. 2 is a timing diagram that illustrates how a low-passed filteredestimate of the laser transmitter rotation rate is first generated byusing the time series of zero crossings for the purposes of the presentinvention.

FIG. 3 illustrates the geometry of the laser beam and observed heightdifference for the purposes of the present invention.

FIG. 4 is an illustration of the laser transmitter-laser detectorgeometry for the purposes of the present invention.

FIG. 5 depicts a diagram that illustrates fan beam planar errors due toslight manufacturing imperfections in optical components for thepurposes of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED AND ALTERNATIVE EMBODIMENTS

Reference will now be made in detail to the preferred embodiments of theinvention, examples of which are illustrated in the accompanyingdrawings. While the invention will be described in conjunction with thepreferred embodiments, it will be understood that they are not intendedto limit the invention to these embodiments. On the contrary, theinvention is intended to cover alternatives, modifications andequivalents that may be comprised within the spirit and scope of theinvention as defined by the appended claims. Furthermore, in thefollowing detailed description of the present invention, numerousspecific details are set forth in order to provide a thoroughunderstanding of the present invention. However, it will be obvious toone of ordinary skill in the art that the present invention may bepracticed without these specific details. In other instances, well knownmethods, procedures, components, and circuits have not been described indetail as not to unnecessarily obscure aspects of the present invention.

The present invention discloses a simplified scheme that makes use ofthe precise timing of the radio-based positioning component of thecombined radio and light based positioning system. This allows one touse a precisely timed single fan beam (instead of dual inclined laserfan beams) to improve the vertical accuracy of the combined radio andlight based positioning system.

FIG. 1 depicts a radio and light based mobile positioning system 10 ofthe present invention comprising: a rover 12 further comprising themobile radio positioning system (Mobile_RADPS) 14 integrated with amobile laser detector 16 and the stationary fan laser transmitter 18integrated with the stationary radio positioning system(Stationary_RADPS) 20. In one embodiment of the present invention, thelaser transmitter 18 is configured to generate a single-rotating laserbeam 22.

The stationary radio positioning system (Stationary_RADPS) receiver 20integrated with the laser transmitter 18 provides a number of benefitsto a potential user comparatively with a system that mechanicallycombines a laser system and a RADPS receiver system. Indeed, thestationary radio positioning system (Stationary_RADPS) receiver 20integrated with the laser transmitter 18 has the reduced cost as opposedto the cost of the combined laser and Stationary_RADPS system becausethe integrated system requires only one set of packaging, can utilize ashared computer memory and can use a common power supply. In theintegrated system the laser beam and the electrical phase center of theStationary_RADPS stationary antenna are separated by the known and fixeddistance ‘d’ 28, wherein in the mechanically combined system thedistance between the laser beam and the electrical phase center of theStationary_RADPS stationary antenna is prone to errors because thisdistance is introduced by an operator of the integrated system.

In one embodiment of the present invention, the stationary radiopositioning system (Stationary_RADPS) 20 is located in a position withknown coordinates. In this embodiment, the coordinates of the lasertransmitter 18 are known in advance.

In one embodiment of the present invention, the stationary radiopositioning system (Stationary_RADPS) 20 is configured to perform theself-surveying in order to obtain its position coordinates 26 and alsothe coordinates of the laser transmitter 18 because the distance ‘d’ 28between the stationary satellite antenna 30 and the laser transmitter isfixed and known.

According to the U.S. Pat. No. 6,433,866 “high precision GPS/RTK andlaser machine control” assigned to the assignee of the presentinvention, the laser transmitter 18 further comprises a plane lasertransmitter configured to generate a reference laser beam 22 providing ahigh accuracy vertical coordinate. The U.S. Pat. No. 6,433,866 isincorporated herein in its entirety.

More specifically, according to the '866 patent, the laser transmitter18 includes a rotating laser system. In a rotating laser system a lasersource spins (mechanically, or optically) in the horizontal plane (orZ-plane). The rotating laser emits a laser beam that provides anaccurate reference plane with a millimeter accuracy. To detect and getbenefit of the rotating laser beam, the potential user has to be locatedwithin vertical range, and has to be equipped with a laser detector (ora laser receiver) 16 capable of receiving the rotating laser beam.Please, see discussion below.

In the mechanical embodiment, the motor physically rotates the laser 18and accordingly the laser beam 22. In the optical embodiment, the mirrorprism rotates in such a way that the physically non-rotating laser emitsthe rotating laser beam.

In one embodiment of the present invention, a 3-D laser stationgenerates at least one rotating fan-shaped laser beam 22. The 3D LaserStation that generates at least one rotating fan-shaped laser beam isdisclosed in U.S. Pat. Nos. 6,870,608 and 6,643,004. Both U.S. Pat. Nos.6,870,608 and 6,643,004 are incorporated herein in their entirety.

Referring still to FIG. 1, the stationary radio positioning system(Stationary_RADPS) receiver 20 can be selected from the group consistingof: {a GPS receiver; a GLONASS receiver; a combined GPS/GLONASSreceiver; a GALILEO receiver; a Global Navigational Satellite System(GNSS) receiver; and a pseudolite receiver}.

The Global Positioning System (GPS) is a system of satellite signaltransmitters that transmits information from which an observer's presentlocation and/or the time of observation can be determined. Anothersatellite-based navigation system is called the Global OrbitingNavigational System (GLONASS), which can operate as an alternative orsupplemental system.

The GPS was developed by the United States Department of Defense (DOD)under its NAVSTAR satellite program. A fully operational GPS includesmore than 24 Earth orbiting satellites approximately uniformly dispersedaround six circular orbits with four satellites each, the orbits beinginclined at an angle of 55° relative to the equator and being separatedfrom each other by multiples of 60° longitude. The orbits have radii of26,560 kilometers and are approximately circular. The orbits arenon-geosynchronous, with 0.5 sidereal day (11.967 hours) orbital timeintervals, so that the satellites move with time relative to the Earthbelow. Generally, four or more GPS satellites will be visible from mostpoints on the Earth's surface, which can be used to determine anobserver's position anywhere on the Earth's surface. Each satellitecarries a cesium or rubidium atomic clock to provide timing informationfor the signals transmitted by the satellites. An internal clockcorrection is provided for each satellite clock.

Each GPS satellite continuously transmits two spread spectrum, L-bandcarrier signals: an L1 signal having a frequency f1=1575.42 MHz(approximately nineteen centimeter carrier wavelength) and an L2 signalhaving a frequency f2=1227.6 MHz (approximately twenty-four centimetercarrier wavelength). These two frequencies are integral multipliesf1=1,540 f0 and f2=1,200 f0 of a base frequency f0=1.023 MHz. The L1signal from each satellite is binary phase shift key (BPSK) modulated bytwo pseudo-random noise (PRN) codes in phase quadrature, designated asthe C/A-code and P-code. The L2 signal from each satellite is BPSKmodulated by only the P-code. The nature of these PRN codes and acceptedmethods for generating the C/A-code and P-code are set forth in thedocument ICD-GPS-200: GPS Interface Control Document, ARINC Research,1997, GPS Joint Program Office, which is incorporated by referenceherein.

The GPS satellite bit stream includes navigational information on theephemeris of the transmitting GPS satellite (which includes orbitalinformation about the transmitting satellite within next several hoursof transmission) and an almanac for all GPS satellites (which includes aless detailed orbital information about all satellites). The transmittedsatellite information also includes parameters providing corrections forionospheric signal propagation delays (suitable for single frequencyreceivers) and for an offset time between satellite clock time and trueGPS time. The navigational information is transmitted at a rate of 50Baud.

A second satellite-based navigation system is the Global OrbitingNavigation Satellite System (GLONASS), placed in orbit by the formerSoviet Union and now maintained by the Russian Republic. GLONASS uses 24satellites, distributed approximately uniformly in three orbital planesof eight satellites each. Each orbital plane has a nominal inclinationof 64.8° relative to the equator, and the three orbital planes areseparated from each other by multiples of 120° longitude. The GLONASSsatellites have circular orbits with a radii of about 25,510 kilometersand a satellite period of revolution of 8/17 of a sidereal day (11.26hours). A GLONASS satellite and a GPS satellite will thus complete 17and 16 revolutions, respectively, around the Earth every 8 days. TheGLONASS system uses two carrier signals L1 and L2 with frequencies off1=(1.602+9 k/16) GHz and f2=(1.246+7 k/16) GHz, where k=(1, 2, . . .24) is the channel or satellite number. These frequencies lie in twobands at 1.597-1.617 GHz (L1) and 1,240-1,260 GHz (L2). The L1 signal ismodulated by a C/A-code (chip rate=0.511 MHz) and by a P-code (chiprate=5.11 MHz). The L2 signal is presently modulated only by the P-code.The GLONASS satellites also transmit navigational data at a rate of 50Baud. Because the channel frequencies are distinguishable from eachother, the P-code is the same, and the C/A-code is the same, for eachsatellite. The methods for receiving and demodulating the GLONASSsignals are similar to the methods used for the GPS signals.

As disclosed in the European Commission “White Paper on Europeantransport policy for 2010”, the European Union will develop anindependent satellite navigation system Galileo as a part of a globalnavigation satellite infrastructure (GNSS).

The GALILEO system is based on a constellation of 30 satellites andground stations providing information concerning the positioning ofusers in many sectors such as transport (vehicle location, routesearching, speed control, guidance systems, etc.), social services (e.g.aid for the disabled or elderly), the justice system and customsservices (location of suspects, border controls), public works(geographical information systems), search and rescue systems, orleisure (direction-finding at sea or in the mountains, etc.).

GALILEO will offer several service levels, from open access torestricted access of various levels:

(A) An open, free basic service, mainly involving applications for thegeneral public and services of general interest. This service iscomparable to that provided by civil GPS, which is free of cost forthese applications, but with improved quality and reliability.

(B) A commercial service facilitating the development of professionalapplications and offering enhanced performance compared with the basicservice, particularly in terms of service guarantee.

(C) A “vital” service (Safety of Life Service) of a very high qualityand integrity for safety-critical applications, such as aviation andshipping. A search and rescue service that will greatly improve existingrelief and rescue services.

(D) A public regulated service (PRS), encrypted and resistant to jammingand interference, reserved principally for the public authoritiesresponsible for civil protection, national security and law enforcementwhich demand a high level of continuity. It will enable securedapplications to be developed in the European Union, and could prove inparticular to be an important tool in improving the instruments used bythe European Union to combat illegal exports, illegal immigration andterrorism.

Reference to a Radio Positioning System (RADPS) herein refers to aGlobal Positioning System, to a Global Orbiting Navigation System, toGALILEO System, and to any other compatible Global NavigationalSatellite System (GNSS) satellite-based system that provides informationby which an observer's position and the time of observation can bedetermined, all of which meet the requirements of the present invention,and to a ground based radio positioning system such as a systemcomprising of one or more pseudolite transmitters.

Referring still to FIG. 1, in one embodiment of the present invention,the Stationary_RADPS receiver 20 utilizes four satellite vehicles SV140, SV2 42, SV3 44, SV4 46 to determine its position coordinates.

A pseudolite comprises a ground based radio positioning system workingin any radio frequency including but not limited to the GPS frequenciesand the ISM (industrial scientific medical) unlicensed operation band,including 900 MHZ, 2.4 GHz, or 5.8 GHz bands ISM bands, or in a radiolocation band such as the (9.5-10) GHz band. Pseudolites can be used forenhancing the GPS by providing increased accuracy, integrity, andavailability.

The complete description of the pseudolite transmitters in GPS band canbe found in ‘Global Positioning System: Theory and Applications; VolumeII”, edited by Bradford W. Parkinson and James J. Spilker Jr., andpublished in Volume 164 in “PROGRESS IN ASTRONAUTICS AND AERONAUTICS”,by American Institute of Aeronautic and Astronautics, Inc., in 1966.

In ISM band, including 900 MHZ, 2.4 GHz, or 5.8 GHz bands, the user canown both ends of the ISM communication system. The ISM technologies aremanufactured by Trimble Navigation Limited, Sunnyvale, Calif. Metricom,Los Gatos, Calif. and by Utilicom, Santa Barbara, Calif.

Pseudolites as radio positioning systems can be configured to operate inISM band.

In one embodiment of the present invention, a pseudolite can beimplemented by using a ground based transmitter that transmits in theGPS band such as the Terralite system designed by Novariant. TheNovariant's Terralite XPS system provides mine managers with directcontrol of the reliability of their positioning systems and helps covergaps in GPS coverage. The Terralite XPS system is comprised of a networkof transmitting stations (Terralites) and mobile receivers. TheTerralites broadcast the XPS positioning signal throughout mines to12-channel, tri-frequency mobile receivers (L1, L2, XPS). The241×173×61-millimeter Terralite receivers weigh 4.5 pounds and utilize 9to 32 volts DC at 22 watts. In XPS mode reported position accuracy is 10centimeters horizontal and 15 centimeters vertical. Novarinat is locatedat Menlo Park, Calif., United States.

The following discussion is focused on a GPS receiver, though the sameapproach can be used for a GLONASS receiver, for a GPS/GLONASS combinedreceiver, GALILEO receiver, or any other RADPS receiver.

Referring still to FIG. 1, in one embodiment of the present invention,the Stationary_RADPS receiver 20 comprises a differential GPS receiver.In differential position determination, many of the errors in the RADPSsignals that compromise the accuracy of absolute position determinationare similar in magnitude for stations that are physically close. Theeffect of these errors on the accuracy of differential positiondetermination is therefore substantially reduced by a process of partialerror cancellation. Thus, the differential positioning method is farmore accurate than the absolute positioning method, provided that thedistances between these stations are substantially less than thedistances from these stations to the satellites, which is the usualcase. Differential positioning can be used to provide locationcoordinates and distances that are accurate to within a few centimetersin absolute terms. The differential GPS receiver can include: (a) a realtime code differential GPS; (b) a post-processing differential GPS; (c)a real-time kinematic (RTK) differential GPS that includes a code andcarrier RTK differential GPS receiver.

The differential GPS receiver can obtain the differential correctionsfrom different sources.

Referring still to FIG. 1, in one embodiment of the present invention,the Stationary_RADPS (differential GPS) receiver 20 can obtain thedifferential corrections from the Base Station 32.

The fixed Base Station (BS) placed at a known location determines therange and range-rate measurement errors in each received GPS signal andcommunicates these measurement errors as corrections to be applied bylocal users. The Base Station (BS) has its own imprecise clock with theclock bias CB_(BASE). As a result, the local users are able to obtainmore accurate navigation results relative to the Base Station locationand the Base Station clock. With proper equipment, a relative accuracyof 5 meters should be possible at distances of a few hundred kilometersfrom the Base Station.

Referring still to FIG. 1, in another embodiment of the presentinvention, the differential GPS receiver 14 can be implemented by usinga TRIMBLE Ag GPS-132 receiver that obtains the differential correctionsfrom the U.S. Cost Guard service free in 300 kHz band broadcast by usingthe wireless communication device 24 and the first wirelesscommunication link 34. In this embodiment, the self-surveying lasertransmitter 18 integrated with the differential GPS receiver 20 shouldbe placed within (2-300) miles from the U.S. Cost Guard Base Station.The accuracy of this differential GPS method is about 50 cm.

Referring still to FIG. 1, in one embodiment of the present invention,the differential corrections can be obtained from the Wide AreaAugmentation System (WAAS) by using the wireless communication device 24and the first wireless communication link 34.

The WAAS system includes a network of Base Stations that uses satellites(initially geostationary satellites-GEOs) to broadcast GPS integrity andcorrection data to GPS users. The WAAS provides a ranging signal thataugments the GPS, that is the WAAS ranging signal is designed tominimize the standard GPS receiver hardware modifications. The WAASranging signal utilizes the GPS frequency and GPS-type of modulation,including only a Coarse/Acquisition (C/A) PRN code. In addition, thecode phase timing is synchronized to GPS time to provide a rangingcapability. To obtain the position solution, the WAAS satellite can beused as any other GPS satellite in satellite selection algorithm. TheWAAS provides the differential corrections free of charge to aWAAS-compatible user. The accuracy of this method is better than 1meter.

Referring still to FIG. 1, in one embodiment of the present invention,the real time kinematic (RTK) differential GPS receiver 20 can be usedto obtain the position locations with less than 2 cm accuracy. The RTKdifferential GPS receiver receives the differential corrections from theBase Station 32 placed in a known location within (10-50) km by usingthe wireless communication device 24 and the first wirelesscommunication link 34. For a high accuracy measurement, the number ofwhole cycle carrier phase shifts between a particular GPS satellite andthe RTK GPS receiver is resolved because at the receiver every cyclewill appear the same. Thus, the RTK GPS receiver solves in real time an“integer ambiguity” problem, that is the problem of determining thenumber of whole cycles of the carrier satellite signal between the GPSsatellite being observed and the RTK GPS receiver. Indeed, the error inone carrier cycle L1 (or L2) can change the measurement result by 19 (or24) centimeters, which is an unacceptable error for the centimeter-levelaccuracy measurements.

Referring still to FIG. 1, in one embodiment of the present invention,the differential corrections can be obtained by the Stationary_RADPSreceiver 20 from the Virtual Base Station (VBS) 32 by using the wirelesscommunication device 24 and the first wireless communication link 34.

Indeed, the Virtual Base Station (VBS) is configured to deliver anetwork-created correction data to a multiplicity of rovers via aconcatenated communications link consisting of a single cellularconnection, and a radio transmission or broadcasting system. Thelocation of the radio transmitting system can be co-located with a GPSBase Station designated as the position of the local Virtual ReferenceStation. This GPS Base Station determines its position using GPS, andtransmits its location to the VRS Base Station via a cellular linkbetween the local GPS Base Station and the VRS Base Station. It enablesthe VRS Base Station to generate differential corrections as if suchdifferential corrections were actually being generated at the real GPSBase Station location. These corrections can be delivered to theself-surveying laser transmitter 18 by using the first wirelesscommunication link 34 and wireless communication device 24.

An article “Long-Range RTK Positioning Using Virtual ReferenceStations,” by Ulrich Vollath, Alois Deking, Herbert Landau, andChristian Pagels, describing VRS in more details, is incorporated hereinas a reference in its entirety, and can be accessed at the followingURL:http://trl.trimble.com/dscgi/ds.py/Get/File-93152/KIS2001-Paper-LongRange.pdf.

Referring still to FIG. 1, in one embodiment of the present invention,the first wireless communication link 34 can be implemented by using avariety of different embodiments.

In general, the first wireless communication link 34 (of FIG. 1) can beimplemented by using a radiowave frequency band, an infrared frequencyband, or a microwave frequency band. In one embodiment, the wirelesscommunication link can include the ISM band, including 900 MHZ, 2.4 GHz,or 5.8 GHz bands, wherein the user can own both ends of the ISMcommunication system.

In one embodiment of the present invention, the first wirelesscommunication link 34 (of FIG. 1) can be implemented by using theTrimble SiteNet™ 900 private radio network. The Trimble SiteNet™ 900private radio network is a rugged, multi-network, 900 MHz radio modemdesigned specifically for the construction and mining industries. It isused to establish robust, wireless data broadcast networks forreal-time, high-precision GPS applications. This versatile Trimble radiooperates in the frequency range of 902-928 MHz, broadcasting, repeating,and receiving real-time data used by Trimble GPS receivers. Underoptimal conditions, the SiteNet 900 radio broadcasts data up to 10 km(6.2 miles) line-of-sight and coverage can be enhanced by using anetwork of multi-repeaters. Using the SiteNet 900 radio as a repeater,enables one to provide coverage in previously inaccessible or obstructedlocations. The SiteNet 900 radio is so versatile, that one can easilychange its operating mode to suit any network configuration. Thisreduces costs and maximizes uptime. Additionally, SiteNet 900 is licensefree in the U.S.A. and Canada, which makes it extremely portable. Onecan move it from project to project without licensing hassles andrestrictions. The SiteNet 900 radio is designed to operate reliably indemanding RF environments where many other products and technologiescannot. Optimized for GPS with increased sensitivity and jammingimmunity, the SiteNet 900 radio also has error correction, and ahigh-speed data rate, ensuring maximum performance. The SiteNet 900radio is especially suited for use with Trimble's SiteVision™ GPS gradecontrol system, and is ideal for all GPS machine control applicationswhere reliability is important. The machine-rugged unit has beendesigned and built especially for harsh construction and miningenvironments. Fully sealed against dust, rain, splash, and spray, theSiteNet 900 radio remains reliable in all weather. The radio'sruggedness and reliability minimizes downtime, lowering ownership costs.Trimble's SiteNet 900 radio can be used with any Trimble GPS receiver,including: MS750, MS850, MS860, and 5700 receivers.

In one embodiment of the present invention, the first wirelesscommunication link 34 (of FIG. 1) can be implemented by using a 1.8 GHzband that supports the personal communications services (PCS). The PCSuses the international standard DCS-1800. Yet, in one more embodiment,the first wireless communication link 34 can include a real time circuitswitched wireless communication link. For instance, the wirelesscommunication link employing a real time circuit switched wirelesscommunication link can include the Iridium satellite system produced byMotorola, Schaumburg, Ill.

In one additional embodiment, the first wireless communication link 34can be implemented by using a system of Low Earth Orbiting Satellites(LEOS), a system of Medium Earth Orbiting Satellites (MEOS), or a systemof Geostationary Earth Orbiting Satellites (GEOS) which can be used tostore and to forward digital packet data. For instance, the LEOS systemsin (20-30) GHz range are manufactured by Cellular Communications locatedin Redmond, Wash., and the LEOS systems in (1.6-2.5) GHz range areproduced by Loral/Qualcomm located in San Diego, Calif.

The first wireless communication link 34 can include a cellulartelephone communication means, a paging signal receiving means, wirelessmessaging services, wireless application services, a wireless WAN/LANstation, or an Earth-satellite-Earth communication module that uses atleast one satellite to relay a radiowave signal. The first wirelesscommunication link 34 can also include the cellular telephonecommunication means that can include an Advanced Mobile Phone System(AMPS) with a modem. The modem can comprise a DSP (digital signalprocessor) modem in 800 MHZ range, or a cellular digital packet data(CDPD) modem in 800 MHZ range. The cellular digital communication meansincludes a means of modulation of digital data over a radiolink using atime division multiple access (TDMA) system employing format IS-54, acode division multiple access (CDMA) system employing format IS-95, or afrequency division multiple access (FDMA). The TDMA system used inEurope is called groupe special mobile (GSM) in French.

For the purposes of the present invention, a cellular telephonecommunication means can be used to get a wireless access to the Internetin order, for example, to broadcast the real time coordinates of theself-surveying laser transmitter 18 position on a special web-site.

Referring still to FIG. 1, the wireless communication device 24 can beimplemented by using any of devices that can be configured to provide:{a cellular link; a radio link; a private radio band link; a SiteNet 900private radio network link; a link to the wireless Internet; and asatellite wireless communication link}. A person skillful in the art caneasily identify all these devices. Please, see the discussion above.

In one embodiment of the present invention, the wireless communicationdevice 24 is configured to respond to specific requests from a mobileequipment (not shown) transmitted over the first wireless communicationlink 34.

Referring still to FIG. 1, in one embodiment of the present invention,the laser transmitter 18 comprises a fan laser transmitter configured togenerate a single rotating fan-shaped laser beam 22 that rotatescontinuously about a vertical axis at a uniform rate above a knownstationary point in the plot of land. The 3-D Laser Station thatgenerates a single rotating fan-shaped laser beam was disclosed in U.S.Pat. Nos. 6,870,608 and 6,643,004.

Referring still to FIG. 1, in one embodiment, the apparatus of thepresent invention 10 further comprises a distance measuring device (notshown) integrated with the laser transmitter 18 and integrated with theStationary_RADPS receiver 20. In this embodiment, the distance measuringdevice (not shown) is configured to measure the distance between thephase center of the stationary radio antenna 30 and a known point orreference plane (not shown) over which the self-surveying lasertransmitter 18 is positioned in order to determine the positioncoordinates of the laser transmitter 18 in relation to the known pointor the reference plane (not shown).

Trimble manufactures a new Spectra Precision Laser HD360, a handhelddistance measurement tool that delivers speed, accuracy and safety tobuilders, engineers and other construction-related contractors. It isespecially useful for measuring distances to hazardous and hard-to-reachlocations. The HD360 is an easy-to-use, portable contractor's tool thatincludes a data display screen and a six-button keypad. Using lasertechnology, it is capable of measuring distance, area and volume,whether indoors or outdoors. The HD360's accuracy is ±3 mm or better, atranges up to 60 meters. The HD360 can be used for building checks andinspections, positioning of building components, building maintenance,alignment and spacing of installation points, installation of drywallsand ceilings, layout from fixed reference points, and calculation ofareas and volumes.

Trimble also manufacturers the HD150 that is ideal for use by generalconstruction and interior contractors, builders, engineers, HVACcontractors and electrical contractors. Its accuracy and otherproductivity enhancing qualities make it the smart choice for a widevariety of applications. Even in hard-to-reach or hazardous locations,such as elevator shafts or open stairways, the HD150 is sufficient forall distance measurement applications.

Above-referenced Trimble devices can be used as wide range of ElectronicDistance Measurement (EDM) tools to implement the distance measurementdevice. More specifically, a special laser “gun” beam can be used tomeasure very precisely the time it takes for a laser beam to make theround-trip from the “gun” to the reflectors, and back. Using this time,the known speed that the laser travels (the speed of light), andcorrecting for air temperature and pressure, the distance can bedetermined to a precision of 1 part per million (i.e. 1 mm over adistance of 1 km).

Referring still to FIG. 1, in one embodiment of the present invention,the rover 12 includes the laser detector 16 and the mobile radiopositioning system (Mobile_RADPS) receiver 14. The Mobile_RADPS receiver14 is selected from the group consisting of: {a GPS receiver; a GLONASSreceiver; a combined GPS/GLONASS receiver; a GALILEO receiver; a GlobalNavigational Satellite System (GNSS) receiver; and a pseudolitereceiver}.

In one embodiment of the present invention, the Mobile_RADPS receiver 14is configured to determine its position coordinates using at least fourradio signals generated by four satellite vehicles SV1 40, SV2, 42, SV344, and SV4 46.

In one embodiment of the present invention, the Mobile_RADPS receiver 14comprises a differential Mobile_RADPS receiver 14. In this embodiment,the second wireless communication link 36 can used to substantiallycontinuously transmit to the differential Mobile_RADPS receiver 14 theprecise coordinate measurements of the laser transmitter 18 and the setof differential corrections obtained by the differentialStationary_RADPS receiver 20. In this embodiment, the differentialMobile_RADPS receiver 14 can utilize the differential corrections toobtain the precise coordinate measurements of the rover 12 and laserdetector 14.

The second wireless communication link 36 can be implemented by using acellular link; a radio link; a private radio band link; a SiteNet 900private radio network link; a link to the wireless Internet; and asatellite wireless communication link.

Referring still to FIG. 1, the laser detector 16 comprises a number ofphoto-diodes. The laser detector 16 measures the signal strength on anumber of photo-diodes to determine the center of a laser beam 22.Trimble manufactures machine mounted laser detectors LR 21 or CR 600that can be used for the purposes of the present invention.

Referring still to FIG. 1, in one embodiment of the present invention,the laser transmitter 18 comprises a single fan-beam system. The beam isrotated about a vertical axis at a very constant angular rate 4 rad/s.The frequency of rotation is given by f (Hz), while the period ofrotation is T seconds. The following relationship exists between theangular parameters:

$\begin{matrix}{\omega = {\frac{2\pi}{T} = {2{\pi \times f_{\lbrack{{rad}/s}\rbrack}}}}} & (1)\end{matrix}$

The laser transmitter 18 head (not shown) is rotated within goodbearings and is driven by a motor which is phase oscillator locked.Furthermore, the laser transmitter head is given sufficient mass toenhance the constant rotation rate of the fan-beam. The present rotationrate is 40 to 50 Hz.

An electronic timing pulse is generated every time the center of thelaser beam 22 passes a zero direction mark (not shown) in the lasertransmitter 18. The timing pulse is accurately (typically to within 40nanoseconds) time tagged within the position coordinates of thetransmitter 18 (determined by the Stationary_RADPS 20) and is denoted τ.

The rotating rate of the laser is typically 50-60 Hz. A low-passedfiltered estimate of the spin rate can be readily generated from thezero-direction crossing times. This information is then transmitted tothe rover unit 12 using the mobile wireless device 38 via the secondwireless data link 36 that is preferably also used for the RADPSdifferential angular rate data.

It will be shown later that variations in the spin rate of the laserdirectly impact on the accuracy of height estimates of the rover 12.Apart from careful manufacture of the rotating laser head, it ispossible to comprise additional timing marks at say every π/4 radians ofrotation where RADPS time stamps are made. Differences between theobserved and expected time-tags at the π/4; π/2; 3π/4 reference pointsprovide a laser correction mechanism for users of the laser signals.

The zero direction crossing times are sent to the rover 12 via thesecond wireless communication link 36. If necessary, additional rotationrate variation parameters can also be comprised.

In one embodiment of the present invention, the rover unit 12 is mountedon a mast 48 for machine control applications, or on a portable pole 48for hand-held construction setup etc, or on the cab of a machine. As wasdisclosed above, the rover 12 includes an integrated laser detector 16and Mobile_RADPS receiver 14 that tracks radio (or satellite signals).The laser detector 16 is capable of detecting the light pulse generatedby the laser transmitter 18. The leading and/or trailing edge of thepulse are time-stamped using the Mobile_RADPS receiver 14 to accuracybetter than 100, typically about 40 nanoseconds.

In one embodiment of the present invention, as was disclosed above, theMobile_RADPS receiver 14 comprises a differential Mobile_RADPS receiverthat receives differential corrections from any other source of thedifferential correction stream.

In one embodiment of the present invention, the differentialMobile_RADPS receiver is capable of computing its location relative tothe laser transmitter 18 to within a few centimeters using real-timekinematic (RTK) techniques. However, the precision of the heightcomponent of the rover is appreciably worse with RADPS techniquescompared with the laser positioning.

In one embodiment of the present invention, the height of the rover 12is determined at the rover's location by using the laser detector 16according to the following procedure.

At the first step, as shown in FIG. 2 in timing diagram 70, a low-passedfiltered estimate of the laser transmitter 18 rotation rate is firstgenerated using the time series of zero crossings:τ(1)72, τ(2)76, τ(3)80, τ(4)84, τ(5)88, . . . τ(n)The timing diagram 70 also illustrates the timings of laser strikest_(strike)(1) 74, t_(strike)(2) 76, t_(strike)(3) 82, and t_(strike)(4)86 at the laser detector's location. Let f_(filt) be the low-passedfiltered rotation frequency, and T_(filt), be the corresponding periodof rotation.

At the next step, the laser detector 16 is configured to measure thetime difference between the received laser pulse (strike) and the lastzero crossing time:t _(diff)(i)=t _(strike)(i)−τ(i);  (2)where:t_(diff)(i)is the difference between the laser strike time at epoch i and thecorresponding zero crossing time;τ(i)is the time of the zero crossing for epoch i;t_(strike)(i)is the time of the laser strike at epoch i.

In practice, laser strikes may be received prior to knowing the lastzero crossing time. This delay is due mainly to the time taken totime-stamp the zero crossing times and broadcast and receive them. Eq.(2) can be modified according to:t _(diff)(i)=t _(strike)(i)−[τ(i−m)+T _(filt) ×m];  (3)where:τ(i−m)is the zero cross time m-rotations ago,T_(filt)is the low-passed filtered rotation period (in seconds),mis an integer number of rotations.

At the next step, the Mobile_RADPS receiver 14 determines the horizontaland vertical rover's location relative to the laser transmitter 18 towithin a few centimeters. The azimuth of the rover unit is then derivedfrom:

$\begin{matrix}{\alpha = {{\tan^{- 1}\left( \frac{E_{T} - E_{R}}{N_{T} - N_{R}} \right)}.}} & (4)\end{matrix}$

In an actual system, one would allow an orientation of the lasertransmitter to be arbitrary and the reference orientation can bedetermined from the measured laser azimuth angle and the GPS vector fromthe stationary to the mobile RADPS.

However, at the following step, assuming the laser transmitter 18 isaligned to true north, and that the laser 18 transmitter and rover 12are at the same height, then the laser strike time will be given by:t _(α)(i)=τ(i)+α(i)×ω;  (5)where:t_(α)(i)is the expected laser strike time for the rover at azimuth α, and at thesame height as the transmitter;α(i) is the azimuth of the rover relative to the transmitter at epoch i;ω is the angular rate of rotation of the transmitter head, as defined inEq. (1).

At the next step, one assumes that, in general, the rover 12 will lieabove or below the height of the laser transmitter 18. If this is thecase, the actual laser strike time will differ from that obtained in Eq.(5). It is this time difference, t_(obs), which enables one to preciselycompute the height of the rover 12, where:t _(obs)(i)=t _(strike)(i)−t _(α)(i).  (6)

FIG. 3 is a diagram 100 that illustrates the geometry of the laser beamand observed the height difference 104 for the purposes of the presentinvention. More specifically, the diagram 100 illustrates the viewlooking back towards the laser transmitter 18 (of FIG. 1) from outsidethe rover 12 (of FIG. 1). The fan beam 108 is inclined at an angle, θradians, 102, as shown. Let point F 106, be the intersection of thefan-beam 108, a horizontal plane at the height of the transmitter 110,and the vertical plane containing the laser detector (D) 114. Point G112, is vertically beneath D 114 and in the same plane as F 106. Theobserved time difference t_(obs), described in Eq. (6) can be convertedto an equivalent angle subtended at the laser transmitter via:φ(i)=ω×t _(obs)(i).  (7)

FIG. 4 illustrates the transmitter-detector geometry 120 for thepurposes of the present invention. The horizontal distance (TG) 122 fromthe transmitter (T) 124 to detector (G) 126 is indirectly observed usingthe Mobile_RADPS 14 (of FIG. 1) to within a few centimeters.

At the next step, with TG 122 known, and the angle FTG . 128 observedEq. (7), the horizontal distance FG 130 can be obtained as follows:

$\begin{matrix}{{FG} = {2{{{TG} \times {\sin\left( \frac{\phi}{2} \right)}}.}}} & (8)\end{matrix}$

The laser determined height difference DG 132 is computed with:DG=FG×tan(θ).  (9)

At the next step, by combining the results from Eq. (7) and Eq. (8) intoEq. (9), a general expression for the laser height can be generated:

$\begin{matrix}{{DG} = {2{{{TG} \times {\sin\left( \frac{\omega\; t_{obs}}{2} \right)} \times {\tan(\theta)}}.}}} & (10)\end{matrix}$

The position coordinates of the rover are interpolated positioncoordinates interpolated between position coordinates taken at GPS timeEpoch immediately preceding the laser strike and position coordinatestaken at GPS time Epoch immediately after the laser strike.

The described above height determination process is affected by a numberof parameters as shown in Eq. (11) below. It is useful to analyze theimpact of the uncertainty in each parameter on the height difference.With this knowledge, it is possible to optimize the system design.

In general,DG=f(TG,ω,t _(obs),θ).  (11)

The total derivative of Eq. (11) is given by:

$\begin{matrix}{{\Delta\;{DG}} = {{\frac{\mathbb{d}f}{\mathbb{d}{TG}}\Delta\;{TG}} + {\frac{\mathbb{d}f}{\mathbb{d}\omega}\Delta\;\omega} + {\frac{\mathbb{d}f}{\mathbb{d}t_{obs}}\Delta\; t_{obs}} + {\frac{\mathbb{d}f}{\mathbb{d}\theta}\Delta\;\theta}}} & (12)\end{matrix}$with the following partial derivatives:

$\begin{matrix}{\frac{\mathbb{d}f}{\mathbb{d}{TG}} = {2 \times {\sin\left( \frac{\omega\; t_{obs}}{2} \right)} \times {\tan(\theta)}}} & (13) \\{\frac{\mathbb{d}f}{\mathbb{d}\omega} = {{TG} \times {\cos\left( \frac{\omega\; t_{obs}}{2} \right)} \times {\tan(\theta)} \times t_{obs}}} & (14) \\{\frac{\mathbb{d}f}{\mathbb{d}t_{obs}} = {{TG} \times {\cos\left( \frac{\omega\; t_{obs}}{2} \right)} \times {\tan(\theta)} \times \omega}} & (15) \\{\frac{\mathbb{d}f}{\mathbb{d}\theta} = {2{{TG} \times {\sin\left( \frac{\omega\; t_{obs}}{2} \right)} \times {\sec^{2}(\theta)}}}} & (16)\end{matrix}$

The table below considers how an error in each parameter contributes tothe total error in the computed height difference DG. The second rowprovides some example parameters for a rover operating 5 meters from thetransmitter and 1.339 m above (or below it). The rotation frequency ofthe laser is taken to be 50 Hz and the beam is inclined at 45 degrees.The partial derivatives of each parameter are shown in row 4.

TABLE 1 Sensitivity parameters for short range operation. TG [m] ω[rad/s] t_(obs) [s] θ [rad] 5.0 314.16 0.000855 0.7854 df/dTG df/dωdf/dt_(obs) df/dθ 0.2678 0.0042 1556.7 2.6780

The RADPS position can readily be obtained to within a few centimetershorizontally, hence TG=0.02 m. The spin rate of the laser transmitter iswell controlled and therefore should have an error of less than 0.5%(Δω=1.5708 rad). With the aid of RADPS, the laser strike should have atiming error of 40 nanoseconds (Δt_(obs)=4.0e-8s)

The beam angle tilt should be known to <0.01 degrees (Δθ=1.745e-4 rad).Using Eq. (12) and the assumed error sources and sensitivities fromTable 1, the total error in height will be:DG=0.0054+0.0066+0.0001+0.0005=0.014 m.

Having a constant spin rate is very important for system performance. Anerror in the spin rate of only 0.5% will lead to 4.2 mm of height errorat a range of 5 m.

Now consider a rover 100 m away from the transmitter, at a heightdifference of 15 m.

TABLE 2 Sensitivity parameters for long range operation. TG [m] ω[rad/s] t_(obs) [s] θ [rad] 100.0 314.16 0.000478 0.7854 df/dTG df/dωdf/dt_(obs) df/dθ 0.150 0.0477 31327.5 30.00

As the distance between the transmitter and rover increase, the systembecomes more sensitive to errors in the various parameters, except theerror in the positions between the base and rover because with a fixederror (say +/−0.01 m) the angular error decreases with increasing range.

Assuming the same level of error sources defined for the short rangecase, the total height error for the long range example will be:DG=0.0030+0.0749+0.0012+0.0052=0.0843 m

The dominant error source in the height error is due to the variation inthe laser rotation rate. In order to obtain a height error of 2 mm, therotation rate of the laser mast be known to 0.04 rad/s (=0.013%).

Some suggestions have already been provided for dealing with variationsin the rotation rate of the rotating laser head using say 8 timingpoints in the rotation. Better still, many tens of calibration pointscould be sampled using the readout of the phase-locked rotation head. Apolynomial could then be fitted to the rotation rate samples and sent tothe user in a laser correction message.

FIG. 5 depicts a diagram 140 that illustrates fan beam planar errors dueto slight manufacturing imperfections in optical components for thepurposes of the present invention.

The following technique for calibrating it out of the system isdisclosed in the present invention. More specifically, with theinstrument setup at a test fixture, a detector is incremented (as shownby the black dots 144 in FIG. 5) through the entire vertical range inthe system. The height determined from the RADPS/laser system iscompared with known calibration heights. The difference between the twoheights provides a measure of the fan-beam planar errors, assuming ofcourse that all other system errors have been appropriately accountedfor.

In one embodiment of the present invention, the position coordinates ofthe implement can be determined with improved accuracy as was disclosedabove. Therefore, the movement of the implement can be controlled, whichcould be important in certain applications. The implement is selectedfrom the group consisting of: {a blade or a bucket on an earthmovingmachine; an agricultural implement; and a device connected to a machine,wherein the device's location is being controlled}.

For instance, in order to detect the plane of light when the rover ismoving over terrain of variable elevation, a laser receiver can bemounted on an electric mast that can move the laser receiver up or downto keep it in the beam. (For instance, the EM21 and LR21 combinationsthat are offered presently by Trimble Navigation Ltd.)

The foregoing description of specific embodiments of the presentinvention have been presented for purposes of illustration anddescription. They are not intended to be exhaustive or to limit theinvention to the precise forms disclosed, and obviously manymodifications and variations are possible in light of the aboveteaching. The embodiments were chosen and described in order to bestexplain the principles of the invention and its practical application,to thereby enable others skilled in the art to best utilize theinvention and various embodiments with various modifications as aresuited to the particular use contemplated. It is intended that the scopeof the invention be defined by the claims appended hereto and theirequivalents.

1. A method of augmenting a mobile radio positioning system (MobileRADPS) by using a stationary fan laser transmitter; wherein a rovercomprises said mobile radio positioning system (Mobile RADPS) integratedwith a mobile laser detector; and wherein said stationary fan lasertransmitter is integrated with a stationary radio positioning system(Stationary RADPS); said method comprising: (A1, 1) self-surveying saidstationary fan laser transmitter to determine its position coordinatesby using said stationary radio positioning system (Stationary RADPS);(A2) rotating said fan laser transmitter about its vertical axis at asubstantially constant angular rate; (A3) generating an electronictiming pulse every time a known position of said laser beam passes areference mark in said laser transmitter; (A4) time-tagging each saidelectronic timing pulse by using said stationary radio positioningsystem (Stationary RADPS); (A5, 1) generating a low-passed filteredestimate of said angular rate of said laser beam by using said pluralityof time tags; wherein each said time tag is indicative of a time instantwhen said reference mark is crossed by one said electronic timing pulse;(A6) transmitting said estimate of said angular rate of said laser beamand said plurality of time tags to said rover via a wirelesscommunication link; wherein said wireless communication link is selectedfrom the group consisting of: {a cellular link; a radio; a private radioband; a SiteNet 900 private radio network; a wireless Internet; asatellite wireless communication link; and an optical wireless link};(B) detecting said single sloping fan beam generated by said stationaryfan laser transmitter by using said mobile laser detector; and (C)timing said fan laser beam strike at said rover's location and usingsaid timing of said fan laser beam strike at said rover's location toimprove accuracy in determination of position coordinates of said rover.2. A method of augmenting a mobile radio positioning system (MobileRADPS) by using a stationary fan laser transmitter; wherein a rovercomprises said mobile radio positioning system (Mobile RADPS) integratedwith a mobile laser detector; and wherein said stationary fan lasertransmitter is integrated with a stationary radio positioning system(Stationary RADPS); said method comprising: (A1) providing saidstationary fan laser transmitter positioned in a location with knowncoordinates; (A2) rotating said fan laser transmitter about its verticalaxis at a substantially constant angular rate; (A7) including at leastone additional reference mark in addition to a main reference mark; (A8)generating an electronic timing pulse every time a known position ofsaid laser beam passes said main reference mark and each said additionalreference mark in said laser transmitter; (A9) time-tagging each saidelectronic timing pulse by using said stationary radio positioningsystem (Stationary_RADPS); (A10) generating an estimate of an angularrate of said laser beam by using a plurality of time tags, wherein eachsaid time tag is indicative of a time instant when said main referencemark is crossed by one said electronic timing pulse, or when each saidadditional reference mark is crossed by one said electronic timingpulse; (A11) transmitting said estimate of said angular rate of saidlaser beam and said plurality of time tags to said rover via saidwireless communication link; wherein a plurality of time tags defined bytime-tagging said laser beam to each said additional reference markcomprises a laser correction data that is configured to compensate forvariation of said rotation angular speed of said laser beam; (B)detecting said single sloping fan beam generated by said stationary fanlaser transmitter by using said mobile laser detector; and (C) timingsaid fan laser beam strike at said rover's location and usin said timingof said fan laser beam strike at said rover's location to improveaccuracy in determination of position coordinates of said rover.
 3. Themethod of claim 2, wherein said step (A10) of generating said estimateof said angular rate of said laser beam by using said plurality of timetags further comprises the step of: (A10, 1) generating a low-passedfiltered estimate of said angular rate of said laser beam by using saidplurality of time tags; wherein each said time tag is indicative of atime instant when said main reference mark is crossed by one saidelectronic timing pulse, or when each said additional reference mark iscrossed by one said electronic timing pulse.